构建高转换效率的纳米探针是推动光声(PA)分子成像发展的关键。传统光声探针的设计思路是使探针在组织光学窗口波段的光吸收系数最大化，而对探针的光声转换性质的研究却未得到足够重视。以金纳米球为例，讨论了在热膨胀机制介导的光声效应中纳米探针的微观光声转换机制，使理性设计高转换效率探针成为可能。通过理论分析和有限元分析发现，由于小尺寸效应，纳米探针不再满足热禁闭条件，在激光脉冲范围内即有热量从球体向周围介质扩散，从而使得纳米探针本身及其周围介质的热膨胀对光声信号均有贡献。

The construction of nanoprobes with high conversion efficiency is the key factor for the development of photoacoustic (PA) molecular imaging. The traditional design methods for PA probes usually maximize their optical absorption at the tissue optical window, while the research on the PA conversion properties of the probes has not been given enough attention. Taking gold nanospheres as an example, the mechanism of microcosmic PA conversion of nanoprobes in PA effect mediated by thermal expansion mechanism is discussed, which makes the rational design of probe with high conversion efficiency possible. Based on theoretical analysis and finite element analysis, it is indicated that nanoprobes no longer satisfy the thermal confinement conditions due to the small size effect. The thermal energy diffuses from the sphere to the surrounding medium in the range of laser pulse. As a result, the PA signal is composed of nanoprobes itself and the thermal expansion of media around the nanoprobes.